This invention relates to coated abrasive products having a resinous binder which holds and supports abrasive granules on a backing sheet.
Coated abrasives generally comprise a flexible backing upon which adhesive holds and supports a coating of abrasive granules. The backing may be paper, cloth, film, vulcanized fiber, etc. or a combination of one or more of these materials. The abrasive granules may be formed of flint, garnet, aluminum oxide, alumina-zirconia, diamond, silicon carbide, etc. Popular present day binders are phenolic resins, hide glue, and varnish. Phenolic resins include those of the phenol-aldehyde type. Besides phenolic resins, hide glue, and varnish, other known resinous binder materials employed in the preparation of coated abrasive products include epoxy resins, ureaformaldehyde resins, and polyurethane resins.
The coated abrasive may employ a "make" coat of resinous binder material which is utilized to secure the ends of the abrasive granules onto the sheet as the granules are oriented and a "size" coat of resinous binder material over the make coat which provides for firm adherent bonding of the abrasive granules to the sheet. The size coat resin may be of the same material as the make coat resin or of a different resinous material.
In the manufacture of coated abrasives, the make coat resinous binder and abrasive granules are first applied to the backing, then the size coat resinous binder is applied, and finally, the construction is fully cured. Generally, thermally curable binders provide coated abrasives having excellent properties, e.g. heat resistance. Thermally curable binders include phenolic resins, epoxy resins, and alkyd resins. With polyester or cellulose backings, however, curing temperatures are limited to about 130.degree. C. At this temperature, cure times are long. The long cure times necessitate the use of festoon curing areas. Disadvantages of festoon curing areas include formation of defects at the suspension rods, inconsistent cure on account of temperature variations in the large festoon ovens, sagging of the binder, and shifting of abrasive granules. Furthermore festoon curing areas require large amounts of space and large amounts of energy.
It has been proposed to use radiation curing processes to avoid the disadvantages of thermal curing processes in the manufacture of coated abrasives. U.S. Pat. No. 4,047,903 discloses an epoxy-acrylic binder and electron irradiation to manufacture coated abrasives. U.S. Pat. Nos. 4,345,545, 4,457,766 and British Pat. No. 2,087,263A disclose a method for electron beam curing of resin coated webs in the manufacture of coated abrasives. Examples of electron beam curable resinous binders disclosed therein include urethane-acrylates and epoxy-acrylates. The binders disclosed in these patents are inferior to thermally curable binders with respect to thermal stability, surface hardness, and grinding performance.